function Hv = F_V(alfa,beta)
k = [cos(alfa)*cos(beta);cos(alfa)*sin(beta);sin(alfa)];
r{1} =[1/4 -1/4 0];
r{2} =[-1/4 -1/4 0];
r{3} =[-1/4 1/4 0];
r{4} =[1/4 1/4 0];

phi = nan(4,1);
for i = 1:4
    phi(i) = 2*pi*r{i}*k;
end;
Hv = exp(1i*phi);
end
